The present invention relates to an electric motor having a stator with a plurality of radially arranged pole shoes between which slots are arranged, a rotor which rotates within the stator and has a rotor shaft which is mounted on both sides of the rotor, isolating stars for covering the end faces of the pole shoes, a stator winding which is situated in the slots and surrounds the end-face isolating stars, and an outer stator casing, and also to a method for the production of an electric motor of this type.
Motors which are as small and as powerful as possible are required for continuous operation of relatively small devices, for example hot-air devices and fans, particularly those used in the manufacturing sector and which must operate continuously. Motors known as universal motors are used in existing devices. Natural wear of the brushes and also of the commutator means that the use of these motors in applications involving continuous operation is limited. In this case, it is possible to introduce electronic commutation but, for design reasons, a different, more powerful motor having the same or even smaller dimensions would then have to be chosen. One option is to use an asynchronous motor, but these are relatively complex to produce and in terms of design have a volume which means an asynchronous motor of current dimensions cannot be installed in hand-held devices of the type in question. Therefore, for this application in particular, electric motors having a diameter of well below 100 mm along with the required power would be desirable. In this context, the journal Schweizer Maschinen Markt (SMM) 31/32, issue 8, 2003, states on pages 149 to 154 that no motor with purely electrical excitation, including amongst others asynchronous machines, is suitable for small drives having a diameter of below 100 mm.
The basic principle of the electric motor specified in the introduction has long been known and is described in DE-C-833 978 and DE-C-967 387. In the case of rotors and stators of electric motors, it is also known to provide an isolating star at the two ends of the rotor or stator formed by laminates being placed against one another (cf. DE-38 42 800-C2 for the rotor of a DC motor). EP-0 445 367-A1 describes an electric motor which has a stator having a plurality of radially arranged magnetic pole pieces. Slots, in which windings are arranged, are located between the magnetic pole pieces. A rotor which rotates within the stator has an isolating arrangement for covering the pole pieces and has an isolating cover which engages over part of the end surface of the rotor which rotates within the stator. The stator winding is wound after the rotor has been inserted into a coil former to which the laminated core of the stator is fitted, with the result that the rotor is wound after the winding has been fitted, but without it being borne in the housing (which will be fitted later) and can no longer be removed.
One object of the present invention is to propose an electric motor with electronic commutation which is suitable for continuous operation, in particular of hot-air devices, at high rotational speeds and also has a diameter in the range considerably less than 100 mm. Another object of the invention is also to propose a hot-air welding device having a motor of this type.